Negative photoresist compositions for the formation of thick films, photoresist films and methods of forming bumps using the same

ABSTRACT

A negative photoresist composition is used for the formation of thick films and includes (A) a novolak resin, (B) a plasticizer, (C) a crosslinking agent and (D) an acid generator. The composition is applied onto a substrate and thereby yields a photoresist film 5 to 100 μm thick. Likewise, the composition is applied onto a substrate of an electronic part, is patterned, is plated and thereby yields a bump.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a negative photoresist composition foruse in the formation of thick films, as well as to a photoresist filmand a method of forming bumps using the photoresist film. Specifically,the invention relates to an alkali-developable negative photoresistcomposition for the formation of thick films which is suitable forphotofabrication such as bump formation, wiring, interlayer insulatingfilm formation, circuit protective film formation and processing andmanufacture of precision parts, carried out when circuit substrates aremanufactured and semiconductors and electronic parts are packaged on thecircuit substrates.

2. Description of the Related Art

The photofabrication is a generic term for techniques in which aphotosensitive resin composition is coated on the surfaces of processarticles and the coating films formed are patterned by photolithography,followed by chemical etching or electrolytic etching using the patternsas masks, or electroforming chiefly using electroplating, any of whichare applied alone or in combination, to fabricate various precisionparts. This is prevalent in the current high-precision microfabricationtechniques.

With the downsizing of electronic equipment, there are a rapid progresstoward higher integration of LSIs and toward ASICs (application specificintegrated circuits), and a demand for multipin thin-film packaging formounting LSIs on electronic equipment, where the bare chip packagingcarried out by the TAB system or flip-chip system, has attracted notice.In such multipin packaging, protruded electrodes of 20 μm or more inheight, called bumps serving as connecting terminals, must be highlyprecisely arranged on the substrate, and it has become more required tomake the bumps higher in precision so as to be adaptable to any furtherminiaturization of LSIs in future. In addition to the formation of theconnecting terminals, a rewiring process is performed to form wiringbetween the chip and the connecting terminals in many cases. In thisprocedure, the wiring is patterned with the use of a thick resist filmabout 5 to about 20 μm in thickness.

Photoresists for the formation of thick films are used as materials forthe formation of such bumps or for rewiring. The term “photoresist forthe formation of thick films” (hereinafter referred to as “thick-filmphotoresist”) used herein means and includes resists that can form filmshaving a thickness of at least about 5 μm on substrates. Using such apatterned thick film as a mask, bumps are formed by plating process.

For example, Japanese Patent Laid-Open Nos. 10-207057, 2000-39709 and2000-66386 disclose thick-film photosensitive resin compositions whichare used for the formation of bumps or for wiring. These conventionalthick-film photosensitive resin compositions require large amounts ofreaction initiators in order to sufficiently react overall of theresulting resist films each having a large thickness. However, largeamounts of reaction initiators may deteriorate compatibility orstability in preservation. Demands have therefore been made on reactioninitiators having higher sensitivity.

Chemically amplified resists containing acid generators have been usedas photosensitive resist compositions having high sensitivity. In thesechemically amplified resists, a protonic acid is generated from theconstitutive acid generator upon irradiation of active light or radiantray and then induces an acid catalytic reaction with a base resin in theresin composition due to heat treatment after exposure. Thus, thechemically amplified resists have significantly higher sensitivity thanconventional resists each having a photoreaction efficiency (a reactionper photon) of less than 1. As an example of chemically amplifiednegative resists, L. E. Bogan et al. disclose a resist usingpolyvinylphenol and a melamine derivative in combination in Proceedingof SPIE, 1086, 34–47 (1989). However, when thick films are formed usingthese chemically amplified resists, the resulting thick films invitecracking and do not exhibit required plating resistance.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a negativephotoresist composition for the formation of thick films, which has highsensitivity and satisfactory plating resistance, is suitable for theformation of thick films and is advantageous as a material for theformation of bumps, as well as to provide a photoresist film and amethod of forming bumps using the photoresist film.

Specifically, the present invention provides, in one aspect, a negativephotoresist composition for the formation of thick films. Thecomposition includes (A) a novolak resin, (B) a plasticizer, (C) acrosslinking agent, and (D) an acid generator.

The ingredient (A) in the composition is preferably an alkali-solublenovolak resin.

The ingredient (B) is preferably an alkali-soluble acrylic resin.

Alternatively, the ingredient (B) may be an alkali-soluble vinyl resin.

In the composition, the ingredient (C) is preferably an alkoxymethylatedamino resin.

The alkoxymethylated amino resin may be selected from methoxymethylatedmelamine resins, ethoxymethylated melamine resins, propoxymethylatedmelamine resins, butoxymethylated melamine resins and combinationsthereof.

The ingredient (D) in the composition is preferably a triazine compound.

The present invention provides, in another aspect, a photoresist filmbeing formed on a substrate by the application of the negativephotoresist composition onto the substrate and having a thickness offrom 5 to 100 μm.

In addition and advantageously, the present invention provides a methodof forming bumps. The method includes the steps of applying the negativephotoresist composition on a substrate of an electronic part to therebyform a resist film as a coating, irradiating the resist film with activelight or radiant ray through a mask having a predetermined pattern,developing the exposed resist film, and plating portions from which theresist film has been removed.

Thus, the present invention provides a negative photoresist compositionfor the formation of thick films, which has high sensitivity andsatisfactory plating resistance, is suitable for the formation of thickfilms and is advantageous as a material for the formation of bumps, aswell as a photoresist film and a method of forming bumps using thephotoresist film.

DETAILED DESCRIPTION OF THE INVENTION

The composition of the present invention will be described below.

Novolak Resins (A)

Novolak resins for use as the ingredient (A) in the present inventionare preferably soluble in alkalis. Such novolak resins (A) can beobtained, for example, by addition condensation of aromatic compoundseach having a phenolic hydroxyl group (hereinafter briefly referred toas “phenols”) with aldehydes in the presence of acid catalysts. Suchphenols for use herein include, but are not limited to, phenol,o-cresol, m-cresol, p-cresol, o-ethylphenol, m-ethylphenyl,p-ethylphenol, o-butylphenol, m-butylphenol, p-butylphenol, 2,3-xylenol,2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xylenol, 3,5-xylenol,2,3,5-trimethylphenol, 3,4,5-trimethylphenol, p-phenylphenol,resorcinol, hydroquinone, hydroquinone monomethyl ether, pyrogallol,fluoroglycinol, hydroxydiphenyl, bisphenol A, gallic acid, gallicesters, α-naphthol, and β-naphthol. The aldehydes include, but are notlimited to, formaldehyde, paraformaldehyde, furfural, benzaldehyde,nitrobenzaldehyde, and acetaldehyde. Catalysts for use in the additioncondensation are not specifically limited and include acid catalystssuch as hydrochloric acid, nitric acid, sulfuric acid, formic acid,oxalic acid, and acetic acid.

The weight average molecular weight of the novolak resin (A) is notspecifically limited but is preferably from 5000 to 30000.

The content of the ingredient (A) is preferably from 50 to 95 parts byweight and more preferably from 65 to 80 parts by weight relative to 100parts by weight of the total amount of the ingredients (A), (B), (C) and(D). If the content of the ingredient (A) is less than 50 parts byweight, the resulting composition may induce deterioration in platingsolution resistance, shapes of bumps and release property. In contrast,if it exceeds 95 parts by weight, the resulting composition may causeimperfect development upon developing.

Plasticizers (B)

Plasticizers for use as the ingredient (B) in the present inventioninclude polymers each having an ethylenic double bond, of which acrylicpolymers and vinyl polymers are preferred. The plasticizers (B) will beillustrated below by taking such an acrylic polymer or vinyl polymer asan example.

Of the ingredients (B) in the present invention, the acrylic polymersare preferably soluble in alkalis and each contain a constitutional unitderived from a polymerizable compound having an ether bond, or aconstitutional unit derived from a polymerizable compound having acarboxyl group.

Such polymerizable compounds having an ether bond include, but are notlimited to, 2-methoxyethyl (meth)acrylate, methoxytriethylene glycol(meth)acrylate, 3-methoxybutyl (meth)acrylate, ethylcarbitol(meth)acrylate, phenoxypolyethylene glycol (meth)acrylate,methoxypolypropylene glycol (meth)acrylate, tetrahydrofurfuryl(meth)acrylate, and other (meth)acrylic acid derivatives each having anether bond and an ester bond, as well as other radical-polymerizablecompounds. Among them, 2-methoxyethyl acrylate and methoxytriethyleneglycol acrylate are preferred. Each of these compounds can be used aloneor in combination.

The polymerizable compounds having a carboxyl group include, but are notlimited to, acrylic acid, methacrylic acid, crotonic acid, and othermonocarboxylic acids; maleic acid, fumaric acid, itaconic acid, andother dicarboxylic acids; 2-methacryloyloxyethyl succinate,2-methacryloyloxyethyl maleate, 2-methacryloyloxyethyl phthalate,2-methacryloyloxyethyl hexahydrophthalate, and other methacrylic acidderivatives each having a carboxyl group and an ester bond. Among them,acrylic acid and methacrylic acid are preferred. Each of these compoundscan be used alone or in combination.

The content of the polymerizable compound having an ether bond in theacrylic polymer is preferably from 30% to 90% by weight, and morepreferably from 40% to 80% by weight. If the content exceeds 90% byweight, the acrylic resin may exhibit deteriorated compatibility withthe novolak resin (A), and the resulting composition may cause Benardconvection cells during prebaking and may fail to yield uniform resistfilms. The Benard cells are irregular pentagonal, hexagonal orheptagonal network patterns formed on the surface of the resist film dueto gradient in gravity or surface tension. If the content is less than30% by weight, the resist film may induce cracks during platingoperation.

The content of the polymerizable compound having a carboxyl group in theacrylic polymer is preferably from 2% to 50% by weight, and morepreferably from 5% to 40% by weight. If the content is less than 2% byweight, the acrylic resin may have decreased solubility in alkalis, theresulting resist film may not be satisfactorily developed, may notsufficiently be striped from the substrate and may remain on thesubstrate. If the content exceeds 50% by weight, the film residual rateafter development and resistance to plating may be deteriorated.

The weight average molecular weight of the acrylic polymer is preferablyfrom 10000 to 800000, and more preferably from 30000 to 500000. If theweight average molecular weight is less than 10000, the resist film maynot have sufficient strength to thereby cause a bulged profile of theplated metal or cracking. If it exceeds 800000, the resist film may havedeteriorated adhesion.

The acrylic polymer may further comprise an additionalradical-polymerizable compound as a monomer in order to appropriatelycontrol the physical and chemical properties of the resultingcomposition. The term “additional radical-polymerizable compound” asused herein means and includes radical-polymerizable compounds otherthan the aforementioned polymerizable compounds. Such additionalradical-polymerizable compounds include, but are not limited to, methyl(meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and otheralkyl esters of (meth)acrylic acid; 2-hydroxyethyl (meth)acrylate,2-hydroxypropyl (meth)acrylate, and other hydroxy-substituted alkylesters of (meth)acrylic acid; phenyl (meth)acrylate, benzyl(meth)acrylate, and other aryl esters of (meth)acrylic acid; diethylmaleate, dibutyl fumarate, and other diesters of dicarboxylic acids;styrene, α-methylstyrene, and other vinyl-group-containing aromaticcompounds; vinyl acetate, and other vinyl-group-containing aliphaticcompounds; butadiene, isoprene, and other conjugated diolefins;acrylonitrile, methacrylonitrile, and other nitrile-group-containingpolymerizable compounds; vinyl chloride, vinylidene chloride, and otherchlorine-containing polymerizable compounds; acrylamide, methacrylamide,and other amide-bond-containing polymerizable compounds. Each of thesecompounds can be used alone or in combination. Among them, n-butylacrylate, benzyl methacrylate and methyl methacrylate are specificallypreferred. The content of the additional radical-polymerizable compoundsin the acrylic polymer is preferably less than 50% by weight and morepreferably less than 40% by weight.

Polymerization solvents for use in the preparation of the acrylicpolymers include, but are not limited to, ethanol, diethylene glycol,and other alcohols; ethylene glycol monomethyl ether, diethylene glycolmonomethyl ether, diethylene glycol ethyl methyl ether, and other alkylethers of polyhydric alcohols; ethylene glycol ethyl ether acetate,propylene glycol methyl ether acetate, and other alkyl ether acetates ofpolyhydric alcohols; toluene, xylene, and other aromatic hydrocarbons;acetone, methyl isobutyl ketone, and other ketones; ethyl acetate, butylacetate, and other esters, of which alkyl ethers of polyhydric alcoholsand alkyl ether acetates of polyhydric alcohols are preferred.

Polymerization catalysts for use in the preparation of the acrylicpolymers include conventional radical-polymerization initiators such as2,2′-azobisisobutyronitrile and other azo compounds; benzoyl peroxide,di-tert-butyl peroxide, and other organic peroxides.

Alternatively, vinyl polymers are preferred as the ingredients (B) inthe present invention. The term “vinyl polymer” as used herein means andincludes polymers obtained from vinyl compounds.

Such vinyl polymers include, but are not limited to, poly(vinylchloride), polystyrenes, polyhydroxystyrenes, poly(vinyl acetate),poly(vinyl benzoate), poly(vinyl alcohol), polyacrylic acid,polymethacrylic acid, polyacrylates, polymaleimide, polyacrylamide,polyacrylonitrile, polyvinylphenol and copolymers thereof.

Among these resins, resins having a carboxyl group or phenolic hydroxylgroup in their side chain or principle chain are alkali-developable andare preferred. Among them, resins each having a carboxyl group arehighly alkali-developable and are typically preferred. The weightaverage molecular weight of the vinyl polymer is preferably from 10000to 200000 and more preferably from 50000 to 100000.

The content of the ingredient (B) in the composition of the presentinvention is preferably from 5 to 30 parts by weight, and morepreferably from 10 to 20 parts by weight, relative to 100 parts byweight of the total amount of the ingredients (A), (B), (C) and (D). Ifthe content of the ingredient (B) is less than 5 parts by weight, theresulting composition may exhibit deteriorated plating solutionresistance and may cause insufficient adhesion and cracking of theresist film during plating operation. If it exceeds 30 parts by weight,the resulting resist film may have deteriorated strength, may yieldinsufficiently sharp profile due to bulging and may exhibit decreaseddefinition.

Crosslinking Agents (C)

Crosslinking agents for use as the ingredient (C) in the presentinvention include, but are not limited to, amino compounds such asmelamine resins, urea resins, guanamine resins, glycoluril-formaldehyderesins, succinamide-formaldehyde resins, and ethylene urea-formaldehyderesins. Among them, alkoxymethylated melamine resins, alkoxymethylatedurea resins and other alkoxymethylated amino resins are preferred. Thealkoxymethylated amino resins can be prepared, for example, in thefollowing manner. Specifically, melamine or urea is allowed to reactwith formaldehyde in a boiling water to thereby yield a condensate, thecondensate is then converted into an ether with a lower alcohol such asmethyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol orisopropyl alcohol, and the resulting reaction mixture is cooled tothereby precipitate an alkoxymethylated amino resin. Examples of thealkoxymethylated amino resins are methoxymethylated melamine resins,ethoxymethylated melamine resins, propoxymethylated melamine resins,butoxymethylated melamine resins, methoxymethylated urea resins,ethoxymethylated urea resins, propoxymethylated urea resins, andbutoxymethylated urea resins. Each of these alkoxymethylated aminoresins can be used alone or in combination. Among them, alkoxymethylatedmelamine resins can stably pattern resists with less changes indimensions of the patterned resists with changes in dose of the activelight or radiant ray and are preferred, of which methoxymethylatedmelamine resins, ethoxymethylated melamine resins, propoxymethylatedmelamine resins and butoxymethylated melamine resins are specificallypreferred.

The content of the ingredient (C) is preferably from 1 to 30 parts byweight and more preferably from 5 to 20 parts by weight relative to 100parts by weight of the total amount of the ingredients (A), (B), (C) and(D). If the content of the ingredient (C) is less than 1 part by weight,the resulting thick film may have deteriorated plating resistance,chemical resistance and adhesion or the resulting bumps may havedeteriorated shapes. In contrast, if it exceeds 30 parts by weight, theresist film may not satisfactorily developed upon developing procedure.

Acid Generators (D)

Acid generators for use as the ingredient (D) in the present inventionare not specifically limited as long as they can directly or indirectlygenerate an acid upon irradiation of light or radiant ray. Such acidgenerators include, but are not limited to,2,4-bis(trichloromethyl)-6-[2-(2-furyl)ethenyl]-s-triazine,2,4-bis(trichloromethyl)-6-[2-(5-methyl-2-furyl)ethenyl]-s-triazine,2,4-bis(trichloromethyl)-6-[2-(5-ethyl-2-furyl)ethenyl]-s-triazine,2,4-bis(trichloromethyl)-6-[2-(5-propyl-2-furyl)ethenyl]-s-triazine,2,4-bis(trichloromethyl)-6-[2-(3,5-dimethoxyphenyl)ethenyl]-s-triazine,2,4-bis(trichloromethyl)-6-[2-(3,5-diethoxyphenyl)ethenyl]-s-triazine,2,4-bis(trichloromethyl)-6-[2-(3,5-dipropoxyphenyl)ethenyl]-s-triazine,2,4-bis(trichloromethyl)-6-[2-(3-methoxy-5-ethoxyphenyl)ethenyl]-s-triazine,2,4-bis(trichloromethyl)-6-[2-(3-methoxy-5-propoxyphenyl)ethenyl]-s-triazine,2,4-bis(trichloromethyl)-6-[2-(3,4-methylenedioxyphenyl)ethenyl]-s-triazine,2,4-bis(trichloromethyl)-6-(3,4-methylenedioxyphenyl)-s-triazine,2,4-bis(trichloromethyl)-6-(3-bromo-4-methoxy)phenyl-s-triazine,2,4-bis(trichloromethyl)-6-(2-bromo-4-methoxy)phenyl-s-triazine,2,4-bis(trichloromethyl)-6-(2-bromo-4-methoxy)styrylphenyl-s-triazine,2,4-bis(trichloromethyl)-6-(3-bromo-4-methoxy)styrylphenyl-s-triazine,2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-1,3,5-triazine,2-(4-methoxynaphthyl)-4,6-bis(trichloromethyl)-1,3,5-triazine,2-[2-(2-furyl)ethenyl]-4,6-bis(trichloromethyl)-1,3,5-triazine,2-[2-(5-methyl-2-furyl)ethenyl]-4,6-bis(trichloromethyl)-1,3,5-triazine,2-[2-(3,5-dimethoxyphenyl)ethenyl]-4,6-bis(trichloromethyl)-1,3,5-triazine,2-[2-(3,4-dimethoxyphenyl)ethenyl]-4,6-bis(trichloromethyl)-1,3,5-triazine,2-(3,4-methylenedioxyphenyl)-4,6-bis(trichloromethyl)-1,3,5-triazine,tris(1,3-dibromopropyl)-1,3,5-triazine,tris(2,3-dibromopropyl)-1,3,5-triazine, and other halogen-containingtriazine compounds; tris(2,3-dibromopropyl)isocyanurate and otherhalogen-containing triazine compounds represented by the followingformula:

wherein R¹, R² and R³ are the same or different and are each ahalogenated alkyl group;α-(p-toluenesulfonyloximino)-phenylacetonitrile,α-(benzenesulfonyloximino)-2,4-dichlorophenylacetonitrile,α-(benzenesulfonyloximino)-2,6-dichlorophenylacetonitrile,α-(2-chlorobenzenesulfonyloximino)-4-methoxyphenylacetonitrile,α-(ethylsulfonyloximino)-1-cyclopentenylacetonitrile; and compoundsrepresented by the following formula:

wherein R⁴ is a monovalent, divalent or trivalent organic group; R⁵ is asubstituted or unsubstituted saturated hydrocarbon group, unsaturatedhydrocarbon group or aromatic compound group; and n is a natural numberof from 1 to 3. The term “aromatic compound group” as used herein meansand includes groups of compounds exhibiting physical and chemicalproperties specific to aromatic compounds, such as phenyl group,naphthyl group and other aromatic hydrocarbon groups; and furyl group,thienyl group and other heterocyclic groups. These groups may each haveone or more appropriate substituents on their rings. Such substituentsinclude, for example, halogen atoms, alkyl groups, alkoxy groups andnitro group. As the group R⁵ preferred are lower alkyl groups eachcontaining from 1 to 4 carbon atoms, such as methyl group, ethyl group,propyl group and butyl group. Among these compounds, compounds in whichR⁴ is an aromatic compound group and R⁵ is a lower alkyl group arepreferred. When n is 1, examples of the acid generators represented bythe formula are compounds of the formula wherein R⁴ is any of phenylgroup, methylphenyl group or methoxyphenyl group and R⁵ is a methylgroup, such as α-(methylsulfonyloximino)-1-phenylacetonitrile,α-(methylsulfonyloximino)-1-(p-methylphenyl)acetonitrile andα-(methylsulfonyloximino)-1-(p-methoxyphenyl)acetonitrile. Examples ofthe acid generators represented by the formula, wherein n is 2, are acidgenerators represented by the following formulae:

The acid generators also include, for example,bis(p-toluenesulfonyl)diazomethane,bis(1,1-dimethylethylsulfonyl)diazomethane, bis(cyclohexylsulfonyl)diazomethane, bis(2,4-dimethylphenylsulfonyl)diazomethane, and otherbissulfonyldiazomethanes; 2-nitrobenzyl p-toluenesulfonate,2,6-nitrobenzyl p-toluenesulfonate, nitrobenzyl tosylate, dinitrobenzyltosylate, nitrobenzyl sulfonate, nitrobenzyl carbonate, dinitrobenzylcarbonate, and other nitrobenzyl derivatives; pyrogallol trimesylate,pyrogallol tritosylate, benzyl tosylate, benzyl sulfonate,N-methylsulfonyloxysuccinimide, N-trichloromethylsulfonyloxysuccinimide,N-phenylsulfonyloxymaleimide, N-methylsulfonyloxyphthalimide, and othersulfonic acid esters; diphenyliodonium hexafluorophosphate,(4-methoxyphenyl)phenyliodonium trifluoromethanesulfonate,bis(p-tert-butylphenyl)iodonium trifluoromethanesulfonate,triphenylsulfonium hexafluorophosphate,(4-methoxyphenyl)diphenylsulfonium trifluoromethanesulfonate,(p-tert-butylphenyl)diphenylsulfonium trifluoromethanesulfonate, andother onium salts; benzoin tosylate, α-methylbenzoin tosylate, and otherbenzoin tosylates; and other diphenyliodonium salts, triphenylsulfoniumsalts, phenyldiazonium salts, and benzyl carbonate. Among these acidgenerators, triazine compounds exhibit high performances as acidgenerators which generate an acid upon irradiation with light, arehighly soluble even when solvents are used and are preferred. Amongthem, bromine-containing triazine compounds are typically preferred, ofwhich 2,4-bis(trichloromethyl)-6-(3-bromo-4-methoxy)phenyl-s-triazine,2,4-bis(trichloromethyl)-6-(3-bromo-4-methoxy)styryl-s-triazine andtris(2,3-dibromopropyl)isocyanurate are specifically preferred.

The content of the ingredient (D) is preferably from 0.01 to 5 parts byweight, more preferably from 0.05 to 1 part by weight and specificallypreferably from 0.1 to 0.5 part by weight relative to 100 parts byweight of the total amount of the ingredients (A), (B), (C) and (D). Ifthe content of the ingredient (D) is less than 0.01 part by weight, thecomposition may not sufficiently be crosslinked and cured by heat orlight and the resulting thick film may have deteriorated platingresistance, chemical resistance and adhesion or the resulting bumps mayhave deteriorated shapes. In contrast, if it exceeds 5 parts by weight,the composition may induce imperfect development upon developingprocedure.

The thick-film photoresist composition of the present invention mayfurther comprise an organic solvent for the adjustment of its viscosity.Such organic solvents include, but are not limited to, ethylene glycolmonomethyl ether, ethylene glycol monoethyl ether, ethylene glycolmonopropyl ether, ethylene glycol monobutyl ether, ethylene glycoldimethyl ether, ethylene glycol diethyl ether, ethylene glycol dipropylether, propylene glycol monomethyl ether, propylene glycol monoethylether, propylene glycol monopropyl ether, propylene glycol monobutylether, propylene glycol dimethyl ether, propylene glycol diethyl ether,diethylene glycol monomethyl ether, diethylene glycol monoethyl ether,diethylene glycol monophenyl ether, diethylene glycol dimethyl ether,diethylene glycol diethyl ether, ethylene glycol monomethyl etheracetate, ethylene glycol monoethyl ether acetate, ethylene glycolmonopropyl ether acetate, ethylene glycol monobutyl ether acetate,ethylene glycol monophenyl ether acetate, diethylene glycol monomethylether acetate, diethylene glycol monoethyl ether acetate, diethyleneglycol monopropyl ether acetate, diethylene glycol monobutyl etheracetate, diethylene glycol monophenyl ether acetate, propylene glycolmonomethyl ether acetate, propylene glycol monoethyl ether acetate,propylene glycol monopropyl ether acetate, 2-methoxybutyl acetate,3-methoxybutyl acetate, 4-methoxybutyl acetate, 2-methyl-3-methoxybutylacetate, 3-methyl-3-methoxybutyl acetate, 3-ethyl-3-methoxybutylacetate, 2-ethoxybutyl acetate, 4-ethoxybutyl acetate, 4-propoxybutylacetate, 2-methoxypentyl acetate, 3-methoxypentyl acetate,4-methoxypentyl acetate, 2-methyl-3-methoxypentyl acetate,3-methyl-3-methoxypentyl acetate, 3-methyl-4-methoxypentyl acetate,4-methyl-4-methoxypentyl acetate, acetone, methyl ethyl ketone, diethylketone, methyl isobutyl ketone, ethyl isobutyl ketone, tetrahydrofuran,cyclohexanone, methyl propionate, ethyl propionate, propyl propionate,isopropyl propionate, methyl 2-hydroxypropionate, ethyl2-hydroxypropionate, methyl 2-hydroxy-2-methylpropionate, methyl3-methoxypropionate, ethyl 3-methoxypropionate, ethyl3-ethoxypropionate, ethyl 3-propoxypropionate, propyl3-methoxypropionate, isopropyl 3-methoxypropionate, ethyl ethoxyacetate,ethyl hydroxyacetate, methyl 2-hydroxy-3-methylbutanoate, methylacetate, ethyl acetate, propyl acetate, isopropyl acetate, butylacetate, isoamyl acetate, methyl carbonate, ethyl carbonate, propylcarbonate, butyl carbonate, methyl pyruvate, ethyl pyruvate, propylpyruvate, butyl pyruvate, methyl acetoacetate, ethyl acetoacetate,benzyl methyl ether, benzyl ethyl ether, dihexyl ether, benzyl acetate,ethyl benzoate, diethyl oxalate, diethyl maleate, γ-butyrolactone,benzene, toluene, xylene, cyclohexanone, methanol, ethanol, propanol,butanol, hexanol, cyclohexanol, ethylene glycol, diethylene glycol andglycerol. Each of these solvents can be used alone or in combination.

In order to form films of at least 20 μm thick by spin coating theresultant negative photoresist composition, the solvent is preferablyused in an amount that provides a solid matter concentration of lessthan or equal to 65% by weight. If the solid matter concentrationexceeds 65% by weight, the composition may have so extremely poorfluidity that it can be handled with difficulty and moreover makes itdifficult to obtain uniform resist films by spin coating.

Where necessary, the composition of the present invention may furthercomprise quenchers such as triethylamine, tributylamine, dibutylamine,triethanolamine, and other secondary or tertiary amines.

Optionally, the composition of the present invention may furthercomprise a surfactant to improve coating properties, defoamingproperties, leveling properties and other properties. Such surfactantsmay be anionic, cationic or nonionic surfactants such asfluorine-containing surfactants commercially available under the tradenames of BM-1000 and BM-1100 (available from BM Chemie GmbH); MEGAFACF142D, MEGAFAC F172, MEGAFAC F173 and MEGAFAC F183 (available fromDainippon Ink & Chemicals, Incorporated); FLUORAD FC-135, FLUORADFC-170C, FLUORAD FC-430 and FLUORAD FC-431 (available from Sumitomo 3MLimited); SURFRON S-112, SURFRON S-113, SURFRON S-131, SURFRON S-141 andSURFRON S-145 (available from Asahi Glass Co., Ltd.); SH-28PA, SH-190,SH-193, SZ-6032 and SF-8428 (available from Toray Silicone Co., Ltd.).The proportion of these surfactants is preferably less than or equal to5 parts by weight relative to 100 parts by weight of the novolak resin(A).

To improve adhesion to the substrate, the composition of the presentinvention may effectively comprise an adhesive aid such as a functionalsilane coupling agent. The term “functional silane coupling agent” asused herein means and includes silane coupling agents each having areactive substituent such as a carboxyl group, methacryloyl group,isocyanate group or epoxy group. Such functional silane coupling agentsinclude, but are not limited to, trimethoxysilylbenzoic acid,γ-methacryloyloxypropyltrimethoxysilane, vinyltriacetoxysilane,vinyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, andβ-(3,4-epoxycyclohexyl)ethyltrimethoxysilane. The proportion of theadhesive aid is preferably less than or equal to 20 parts by weightrelative to 100 parts by weight of the novolak resin (A).

To finely adjust the solubility to an alkali developing solution, thecomposition of the present invention may comprise an acid or acidanhydride and/or a high boiling solvent. Such acids or acid anhydridesinclude, but are not limited to, monocarboxylic acids such as aceticacid, propionic acid, n-butyric acid, iso-butyric acid, n-valeric acid,iso-valeric acid, benzoic acid, and cinnamic acid; hydroxymonocarboxylicacids such as lactic acid, 2-hydroxybutyric acid, 3-hydroxybutyric acid,salicylic acid, m-hydroxybenzoic acid, p-hydroxybenzoic acid,2-hydroxycinnamic acid, 3-hydroxycinnamic acid, 4-hydroxycinnamic acid,5-hydroxyisophthalic acid and syringic acid; polyhydric carboxylic acidssuch as oxalic acid, succinic acid, glutaric acid, adipic acid, maleicacid, itaconic acid, hexahydrophthalic acid, phthalic acid, isophthalicacid, terephthalic acid, 1,2-cyclohexanedicarboxylic acid,1,2,4-cyclohexanetricarboxylic acid, trimellitic acid, pyromelliticacid, cyclopentanetetracarboxylic acid, butanetetracarboxylic acid and1,2,5,8-napthalenetetracarboxylic acid; and acid anhydrides such asitaconic anhydride, succinic anhydride, citraconic anhydride,dodecenylsuccinic anhydride, tricarbanilic anhydride, maleic anhydride,hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, himicanhydride, 1,2,3,4-butanetetracarboxylic anhydride,cyclopentanetetracarboxylic dianhydride, phthalic anhydride,pyromellitic anhydride, trimellitic anhydride,benzophenonetetracarboxylic anhydride, ethylene glycolbisanhydrotrimellitate and glycerol trisanhydrotrimellitate. Such highboiling solvents include, but are not limited to, N-methylformamide,N,N-dimethylformamide, N-methylformanilide, N-methylacetamide,N,N-dimethylacetamide, N-methylpyrrolidone, dimethylsulfoxide, benzylethyl ether, dihexyl ether, acetonylacetone, isophorone, caproic acid,caprylic acid, 1-octanol, 1-nonanol, benzyl alcohol, benzyl acetate,ethyl benzoate, diethyl oxalate, diethyl maleate, γ-butyrolactone,ethylene carbonate, propylene carbonate and phenyl cellosolve acetate.The amount of such a substance is not specifically limited and may beset in accordance with purposes and coating processes of the resultingcomposition, as long as the composition can be uniformly mixed. Ingeneral, the amount of the substance is preferably less than or equal to60% by weight, and more preferably less than or equal to 40% by weight,based on the weight of the resulting composition.

The composition of the present invention may further comprise otheradditives such as a filler, a coloring agent and a viscosity modifieraccording to necessity. Such fillers include, but are not limited to,silica, alumina, talc, bentonite, zirconium silicate and powdered glass.The coloring agent includes, but is not limited to, extender pigmentssuch as alumina white, clay, barium carbonate and barium sulfate;inorganic pigments such as zinc white, white lead, chrome yellow, redlead, ultramarine blue, iron blue, titanium oxide, zinc chromate, rediron oxide and carbon black; organic pigments such as Brilliant Carmine6B, Permanent Red 6B, Permanent Red R, Benzidine Yellow, PhthalocyanineBlue and Phthalocyanine Green; basic dyes such as magenta and rhodamine;direct dyes such as Direct Scarlet and Direct Orange; and acid dyes suchas Rhocerin and Metanil Yellow. The viscosity modifier includes, forexample, bentonite, silica gel and powdered aluminum. These additivesmay be used in such an amount that they do not deteriorate the essentialproperties of the composition, and preferably less than or equal to 50%by weight based on the weight of the resulting composition.

The composition of the present invention may further compriseantifoaming agents and other additives according to necessity. Suchantifoaming agents include, for example, silicone-containing orfluorine-containing antifoaming agents.

The composition of the present invention may be prepared by only mixingand stirring the materials according to a conventional procedure whenthe filler and the pigment are not used. When the filler and the pigmentare used, the materials may be dispersed and mixed by means of adispersion machine such as a dissolver, a homogenizer or a three-rollmill, further optionally followed by filtration using a mesh filter or amembrane filter.

The composition of the present invention is suitable for the formationof thick films and can also be used in, for example, protective filmsformed when various substrates such as copper, chromium, iron and glasssubstrates are etched, and resists for semiconductor fabrication.

When the composition of the present invention is used for the formationof a photoresist film, the thickness of the resulting film is from 5 to100 μm, preferably from 5 to 40 μm, and more preferably from 20 to 30μm.

Using the composition of the present invention as a resist film, bumpscan be formed, for example, in the following manner.

-   (1) Formation of Coating: A solution of the composition prepared as    described above is applied on a substrate having a predetermined    wiring pattern to a thickness of 5 to 100 μm and preferably 20 to 40    μm, and the applied film is heated (prebaked) to remove the solvent    to form a coating. To coat the composition on the substrate, a    process such as spin coating, roll coating, screen printing or    applicator coating may be employed. Prebaking conditions may differ    depending on the types of the respective components in the    composition, their mixing proportion and the coating layer    thickness. Usually the prebaking may be carried out at 70° C. to    130° C., and preferably 80° C. to 120° C., for 2 to 60 minutes.-   (2) Exposure to Radiant Rays: The coating thus formed is exposed to    radiant rays such as ultraviolet rays or visible light rays of 300    to 500 nm in wavelength through a mask with a predetermined pattern,    to expose the coating only at its wiring pattern areas on which    bumps are to be formed. Such radiation sources include, for example,    low-pressure mercury lamps, high-pressure mercury lamps,    ultrahigh-pressure mercury lamps, metal halide lamps, and argon gas    lasers. The radiant rays to which the coating is exposed are, for    example, ultraviolet rays, visible light rays, far ultraviolet rays,    X-rays and electron beams. Radiation dose may differ depending on    the types of the respective components in the composition, their    mixing proportion and the coating layer thickness. For example, when    the ultrahigh-pressure mercury lamps are used, the radiation dose is    from 100 to 2000 mJ/cm².-   (3) Heating: After the exposure to radiant rays, the coating is    heated according to a conventional procedure.-   (4) Development: After heating, the pattern is developed by    dissolving and removing the unexposed unnecessary areas, using an    alkaline solution as a developing solution, to make only the    radiation-exposed areas remain. As the developing solution, an    aqueous solution of a basic compound may be used; the basic compound    includes, for example, sodium hydroxide, potassium hydroxide, sodium    carbonate, sodium silicate, sodium metasilicate, aqueous ammonia,    ethylamine, n-propylamine, diethylamine, di-n-propylamine,    triethylamine, methyldiethylamine, dimethylethanolamine,    triethanolamine, tetramethylammonium hydroxide, tetraethylammonium    hydroxide, pyrrole, piperidine, 1,8-diazabicyclo[5.4.0]-7-undecene,    and 1,5-diazabicyclo[4.3.0]-5-nonane. An aqueous solution prepared    by adding to the aqueous solution of any of these basic compounds a    water-soluble organic solvent, such as methanol or ethanol, or a    surfactant may also be used as the developing solution.

Development time may differ depending on the types of the respectivecomponents in the composition, their mixing proportion and the driedcoating thickness of the composition. Usually development may be carriedout for 1 to 30 minutes, and may be carried out by any of dispensingdevelopment, dip development, puddle development and spray development.After the development, the substrate is rinsed with running water for 30to 90 seconds, followed by air drying by means of an air gun or dryingin an oven.

The plating process is not specifically limited, and any conventionalplating processes can be used.

EXAMPLES

The present invention will be illustrated in further detail withreference to several examples and comparative examples below, which arenot intended to limit the scope of the invention. All parts andpercentages are by weight unless otherwise specified.

Synthesis Example 1 Synthesis of Alkali-soluble Novolak Resin (A)

Sixty parts of m-cresol was added to forty parts of p-cresol, theresulting mixture was condensed with formaldehyde (as formalin) using anoxalic acid catalyst according to a conventional procedure and therebyyielded a cresol novolak resin. Low molecular weight fractions of theresin were removed by fractionation to yield an alkali-soluble novolakresin having a weight average molecular weight of 15000 (novolak resinA).

Synthesis Example 2 Synthesis of Alkali-Soluble Acrylic Resin (B)

The inside of a flask equipped with a stirrer, reflux condenser,thermometer and dropping funnel was replaced by nitrogen gas, and 200 gof propylene glycol methyl ether acetate as a solvent was placed in theflask, followed by stirring. Thereafter, the temperature of the solventwas raised to 80° C. Into the dropping funnel, 0.5 g of2,2′-azobisisobutyronitrile as a polymerization initiator (availablefrom Wako Pure Chemical Industries, Ltd. under the trade name of V-65),130 g of 2-methoxyethyl acrylate, 50.0 g of benzyl methacrylate and 20.0g of acrylic acid were charged, followed by stirring until thepolymerization initiator dissolved. The resulting solution was uniformlydropped into the flask over 3 hours and was allowed to react at 80° C.for further five hours. The reaction mixture was then cooled to roomtemperature and thereby yielded an acrylic resin (alkali-soluble acrylicresin B).

Example 1

In 150 parts of propylene glycol methyl ether acetate were dissolved 75parts of the novolak resin A, 15 parts of the alkali-soluble acrylicresin B, 10 parts of hexamethoxymethylated melamine (available fromSanwa Chemical Co., Ltd. under the trade name of Nikalac Mw-100) as acrosslinking agent (C) and 0.3 part of an acid generator (D) representedby the following formula, the resulting solution was filtrated using amembrane filter having a pore size of 1.0 μm and thereby yielded anegative photoresist composition. The properties of this compositionwere determined according to procedures mentioned later. The results areshown in Table 1.

Example 2

A negative photoresist composition was prepared in the same manner as inExample 1, except that 70 parts of the novolak resin A and 20 parts ofthe alkali-soluble acrylic resin B were used. The properties of thiscomposition were determined according to the procedures mentioned later.The results are shown in Table 1.

Example 3

A negative photoresist composition was prepared in the same manner as inExample 1, except that 80 parts of the novolak resin A and 10 parts ofthe alkali-soluble acrylic resin B were used. The properties of thiscomposition were determined according to the procedures mentioned later.The results are shown in Table 1.

Example 4

A negative photoresist composition was prepared in the same manner as inExample 1, except that 15 parts of an alkali-soluble ethyl vinyl etherpolymer obtained by subjecting ethyl vinyl ether to polymerizationreaction in the presence of a catalyst in a gaseous phase at hightemperature and high pressure was used as the plasticizer (B). Theproperties of this composition were determined according to theprocedures mentioned later. The results are shown in Table 1.

Example 5

A negative photoresist composition was prepared in the same manner as inExample 1, except that 15 parts of an alkali-soluble methyl vinyl etherpolymer obtained by subjecting methyl vinyl ether to polymerizationreaction in the presence of a catalyst in a gaseous phase at hightemperature and high pressure was used as the plasticizer (B). Theproperties of this composition were determined according to theprocedures mentioned later. The results are shown in Table 1.

Comparative Example 1

A negative photoresist composition was prepared in the same manner as inExample 1, except that the ingredient (B) was not used. The propertiesof this composition were determined according to the proceduresmentioned later. The results are shown in Table 2.

Comparative Example 2

A negative photoresist composition was prepared in the same manner as inExample 1, except that the crosslinking agent (C) and the acid generator(D) were not used and that 15 parts of a conventional photoreactioninitiator, i.e., a photoreaction initiator obtained by allowing 1 moleof a compound represented by the following formula to react with 2 molesof 1,2-naphthoquinonediazido-4-sulfonyl chloride. The properties of thiscomposition were determined according to the procedures mentioned below.The results are shown in Table 2.

Determination of Properties

(i) Compatibility

A sample negative photoresist composition was stirred for 12 hours, andthe state of the solution immediately after stirring and upon leavingfor 12 hours after the completion of stirring was visually observed. Howit stood as a dispersion was determined according to the followingcriteria:

Good: The composition was seen to have been uniformly dissolvedimmediately after stirring, and also seen to be in the uniformlydissolved state even after 12 hours.

Fair: The composition was seen to have been uniformly dissolvedimmediately after stirring, but seen to have caused phase separationafter 12 hours.

Poor: The composition was not in the uniformly dissolved state evenimmediately after stirring.

(ii) Coating Property

The above negative photoresist composition used in the test (i) wascoated on a 5 inch gold-sputtered silicon wafer by means of a spinner at1000 rpm for 25 seconds, and the coating formed was heated at 110° C.for 6 minutes on a hot plate. The surface of the dry film was visuallyobserved to determine coating property according to the followingcriteria:

Good: The film formed was free of unevenness and was uniform.

Poor: The film formed had unevenness such as pinholes and cissing.

(iii) Developing Property and Definition

The sample negative photoresist composition was coated on a 5-inchsilicon wafer by means of a spinner at 1000 rpm for 25 seconds, and thecoating formed was prebaked at 110° C. for 6 minutes on a hot plate andthereby yielded a coating about 20 μm thick. Next, through a patternedmask for measuring definition, the coating, which was formed on onesheet of coated substrate dividedly in three regions using a stepper(available from Ultratech under the trade name of Saturn Spectrum 3Wafer Stepper), was exposed to ultraviolet rays at radiation dosesranging from 200 mJ/cm² to 2000 mJ/cm², respectively. The exposedsubstrate was heated at 110° C. for 6 minutes and was then subjected todevelopment using a developing solution (available from Tokyo Ohka KogyoCo., Ltd. under the trade name of PMER Series P-7G). The resulting filmwas rinsed with running water, followed by nitrogen blowing to yield apatternwise cured product. This was observed on an optical microscope todetermine the definition according to the following criteria:

Good: A hole pattern of 5 μm square had been resolved at any of theabove radiation doses and no residue was observed.

Poor: A hole pattern of 5 μm square had not been resolved or any residuewas observed.

(iv) Plating Solution Resistance

The substrate having the patternwise cured product prepared in the abovetest (iii) was made into test materials. The test materials weresubjected to ashing with oxygen plasma, was immersed in a non-cyanogengold sulfite plating solution at 70° C. for 90 minutes, was then rinsedwith running water and thereby yielded processed test materials. Theprocessed test materials were observed on an optical microscope or anelectron microscope to examine how the patternwise cured product stood,to determine the shape of the bumps and the plating solution resistanceof the patternwise cured product according to the following criteria.

Good: The bumps and the patternwise cured product showed no particularchanges.

Poor: Cracks, bulges or chips occurred in the patternwise cured productor the patternwise cured product had a rough surface.

(v) Bump Shape

Processed test materials were prepared in the same manner as in the test(iv) and were observed on an optical microscope or an electronmicroscope to examine the shapes of the bumps according to the followingcriteria:

Good: The shapes of the bumps were good and were in accordance with thatof the patternwise cured product.

Poor: The shapes of the bumps were not in accordance with that of thepatternwise cured product and induced bulging.

(vi) Releasability

The substrates each carrying the patternwise cured product obtained inthe test (iii) were used as test materials, were immersed in a releasingagent (available from Tokyo Ohka Kogyo Co., Ltd. under the trade name ofStripper 710) at room temperature for 5 minutes with stirring, wererinsed with running water to thereby stripe the patternwise curedproduct. The resulting substrates were observed visually or on anoptical microscope to examine the releasability of the patternwise curedproduct according to the following criteria:

Good: No residue of the patternwise cured product remained on thesubstrate.

Poor: The residue of the patternwise cured product remained on thesubstrate.

(vii) Photosensitivity

The sample negative photoresist composition was applied onto a 5-inchsilicon wafer and thereby yielded a coating about 40 μm thick. Next,through a patterned mask for measuring definition, the coating, whichwas formed on one sheet of coated substrate dividedly in three regionsusing a stepper (available from Ultratech under the trade name of SaturnSpectrum 3 Wafer Stepper), was exposed to ultraviolet rays at dosesranging from 200 mJ/cm² to 10000 mJ/cm², respectively. The exposedsubstrate was then subjected to development using a developing solution(available from Tokyo Ohka Kogyo Co., Ltd. under the trade name of PMERSeries P-7G). The resulting film was rinsed with running water, followedby nitrogen blowing to yield a patternwise cured product. This wasobserved on an optical microscope. In this procedure, thephotosensitivity was defined as the dose at which a hole pattern of 5 μmsquare was resolved and no residue was observed.

TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Compatibility Good Good Good GoodGood Coating property Good Good Good Good Good Developing property andGood Good Good Good Good definition Plating solution Good Good Good GoodGood resistance Bump shape Good Good Good Good Good releasability GoodGood Good Good Good Photosensitivity 1000 1000 1000 1000 1000 (mJ/cm²)

TABLE 2 Com. Ex. 1 Com. Ex. 2 Compatibility Good Good Coating propertyGood Good Developing property and Good Good definition Plating solutionresistance Poor (cracks) Good Bump shape Poor (creeping) GoodReleasability Good Good Photosensitivity (mJ/cm²) 1000 5000

The composition according to Comparative Example 2 had significantlydeteriorated photosensitivity, although it stood comparison in the otherproperties with the compositions according to Examples 1 through 5.

Other embodiments and variations will be obvious to those skilled in theart, and this invention is not to be limited to the specific mattersstated above.

1. A negative photoresist composition for the formation of thick films,comprising: (A) a novolak resin; (B) a plasticizer selected from thegroup consisting of an alkali-soluble ethyl vinyl ether polymer and analkali-soluble methyl vinyl ether polymer and having a weight-averagemolecular weight of 10,000–200,000; (C) a crosslinking agent; and (D) anacid generator; wherein the composition is a composition for formingbumps by plating, wherein the ingredient (C) is an alkoxymethylatedamino resin.
 2. The composition according to claim 1, wherein theingredient (A) is an alkali-soluble novolak resin.
 3. The compositionaccording to claim 1, wherein the alkoxymethylated amino resin is oneselected from the group consisting of methoxymethylated melamine resins,ethoxymethylated melamine resins, propoxymethylated melamine resins,butoxymethylated melamine resins and combinations thereof.
 4. Thecomposition according to claim 1, wherein the ingredient (D) is atriazine compound.
 5. A photoresist film being formed on a substrate bythe application of the negative photoresist composition as claimed inclaim 1 onto the substrate and having a thickness of from 5 to 100 μm.6. A method of forming bumps, the method comprising the steps of:applying the negative photoresist composition as claimed in claim 1 on asubstrate of an electronic part to thereby form a resist film as acoating; irradiating the resist film with active light or radiant raythrough a mask having a predetermined pattern; developing the exposedresist film; and plating portions from which the resist film has beenremoved.
 7. The composition according to claim 1, wherein theplasticizer has a weight-average molecular weight of 50,000–100,000. 8.A photoresist film being formed on a substrate by the application of anegative photoresist composition onto the substrate and having athickness of from 5 to 100 μm, wherein the negative photoresistcomposition is a negative photoresist composition for the formation ofthick films, comprising: (A) a novolak resin; (B) a plasticizer selectedfrom the group consisting of an alkali-soluble ethyl vinyl ether polymerand an alkali-soluble methyl vinyl ether polymer and having aweight-average molecular weight of 10,000–200,000; (C) a crosslinkingagent; and (D) an acid generator; wherein the composition is acomposition for forming bumps by plating, wherein the substrate is agold-sputtered wafer.